(1) Field of the Invention
This invention relates to devices known in the art as "twistlocks", which are devices for use to locate and lock I.S.O. freight transport containers (and equivalent containers built to other standards) in position on road vehicle trailers, railway wagons, and the like.
A twistlock normally comprises two essential components: (1) a locating block or "register"; and (2) a T-headed bolt or "anvil bolt". The register provides lateral location and restraint to the respective corner fitting of the I.S.O. container. The centre of the register normally has a hole which accommodates the stem of the anvil bolt, with the head of the anvil bolt being located just above the top of the register. The register is very approximately rectangular in plan. By turning the anvil bolt vertically around its stem (protruding up through the middle of the register), the T-shaped head of the anvil bolt can be either aligned with the register, or turned cross-ways thereto. When the register and the bolt head are aligned, an I.S.O. container can be lowered onto and fitted over the bolt and register, or lifted away from them. When the bolt head is turned cross-ways to the register with an I.S.O. container in place, the container is latched in place (assuming the register and the anvil bolt to be suitably anchored). Such twistlocks are well known, both for I.S.O. containers, and for containers complying with other standards.
Some trailer manufacturers prefer that the twistlocks which they install on trailers manufactured by them are purchased by them as ready-made units which are then installed by welding the unit directly into place, rather than by bolt-mounting a unit through a mounting bracket thereof. This is particularly the case where the twistlocks are not intended to be retractable into the carrying deck of the relevant vehicle, nor otherwise lowered to positions in which the twistlocks do not protrude from the deck.
(2) Description of the Prior Art
A welded-in non-retractable twistlock is described by Schulz et al in U.S. Pat. No. 4,697,967, the disclosure of which is incorporated herein by reference.
The various form of twistlock disclosed by Schulz et al in U.S. Pat. No. 4,697,967 all have a register which is integral with a mounting boss by which the twistlock is welded into its operational location. This integral component provides the through-bore in which the anvil bolt is rotatable, and further provides the static part of latching means by which the anvil bolt is rotationally latched in its two rotational positions, one such rotational position being rotational alignment of the bolt head with the register for placement or removal of the container, and the other rotational position being rotational misalignment (typically by about 70 degrees) of the bolt head with the register for latching of the container by the twistlock.
Thus this integral component of the Schulz et al twistlocks requires particularly careful alignment during welding thereof into place, and further requires precautions to be taken against undesirable distortions being induced by the welding procedure, such as might cause failure of the anvil bolt to pivot properly therein and/or failure of the rotational latching mechanism of the twistlock.
It is therefore an object of the invention to provide a welded-in non-retractable twistlock which is free of such disadvantages.